1. Field of the Invention
This invention relates to a fixing belt for use in image forming apparatus such as electrophotographic machines, facsimile machines and printers.
2. Prior Art
Known examples of prior art fixing belts used in such image forming apparatus include a belt based on fluororesin film and a belt prepared by coating a heat resistant resin film on its surface with a silicone rubber composition followed by heat curing as disclosed in Japanese Patent Application Kokai (JP-A) No. 115279/1992.
The fixing belt based on fluororesin is too hard to follow fine irregularities when used in image forming apparatus. In fixing an image on recording paper through application of heat and pressure, the image once transferred to the recording paper can be transferred back to the belt, resulting in a lowering of image quality.
The fixing belt in the form of a heat resistant resin film having a silicone rubber layer formed on its surface has the advantage that toner release is improved due to a small amount of silicone oil in the silicone rubber. Since bleeding of the oil is limited, however, the toner release experiences a change with time. Without a supply of additional silicone oil, it is difficult to completely suppress the phenomenon of reverse transfer of an image from the recording paper to the fixing belt. Especially existing color image forming apparatus such as color copying machines cannot dispense with supply of silicone oil. Problems arise when a belt having an outermost layer formed of silicone rubber which can be swollen by silicone oil is used in color image forming apparatus.